1. Field of the Invention
The present invention relates to a valve operating system in an internal combustion engine.
2. Description of the Prior Art
A valve operating system in an internal combustion engine is conventionally already known, for example, from Japanese Patent Application Laid-open No. 229912/86, which comprises a hydraulic transmitting means which is capable of hydraulically transmitting the operating force and is provided between an operating-force generating means for generating an operating force corresponding to the revolution of the engine and an operating-force applying means for operating an engine valve.
The above prior art valve operating system has an advantage that the opening and closing characteristic of the engine valve can be accurately controlled by varying the operating-force transmitting mode of the hydraulic transmitting means by the control of the hydraulic pressure. On the other hand, a slide member having an extremely small clearance is required for the hydraulic transmitting means in order to convert the hydraulic pressure into the operating force. When the introduction of a working oil having an extremely low temperature or an inappropriate viscosity results in an abnormally increased viscosity of the working oil, the slide member is accompanied by a large resistance to the operation due to a resistance to the sliding movement thereof in the clearance area and a resistance to the flow of the working oil having an abnormally high viscosity and hence, a delay may be produced in the operation of the engine valve in some cases. When an abnormal closing of an oil passage in the hydraulic transmitting means, an abnormality of an oil supply source or the like is produced, it is difficult to transmit the operating force by the hydraulic transmitting means.
There is also a conventionally known valve operating system which comprises a mechanical transmitting means for mechanically transmitting the operating force between the operating-force generating means and the operating-force applying means, as disclosed in Japanese Patent Publication No. 7005/91. In this system, a reliable transmittion of the operating force is possible, but it is difficult to accurately control the opening and closing characteristic of the engine valve.